Most motor vehicles incorporate suspension systems that employ struts. Generally, associated with these struts is a hydraulic damper or shock absorber having a telescoping rod extending therefrom. During operation, the telescoping rod moves into and out of a shell forming part of the shock absorber. As the rod nears the end of its travel, a point referred to by those skilled in the pertinent art to which the invention pertains as "full jounce", an auxiliary spring retards the rod's travel by engaging the shock absorber gradually slowing, and then stopping the rod's motion. It is important that the auxiliary spring decelerates and stops the rod's retrograde motion in a manner that ensures a smooth ride for the vehicle.
In order to effect the above-described retardation of the rod's motion in as smooth a manner as is possible, it is desirable that the auxiliary spring exhibit characteristics consistent with a variable or non-linear spring rate.
In general, known auxiliary springs are elastomeric and of various shapes and configurations, and most are fabricated from rubber which, at best, displays a spring rate curve having two distinct deflections, but which does not behave in a non-linear manner.
In addition to motor vehicles, bicycles, especially those referred to as mountain bikes, often employ suspension systems for absorbing impact-type or shock loads. However, these suspension systems are often too stiff, providing inadequate shock absorption, or too soft, causing the same problem. It is difficult or even impossible to provide a suspension that can provide adequate shock absorption for a wide range of differing conditions. Accordingly, there is a need for a suspension system providing a range of shock absorbing properties adequate for accommodating a plurality of different terrain.
Spring systems comprised of solid elastomers have been proposed. U.S. Pat. No. 4,962,916 (the '916 patent) to Palinkas, assigned to the assignee of the present invention, and incorporated by reference herein in its entirety, discloses an elastomeric spring comprising hollow elastomeric tubes stacked upon one another with the axes of the tubes normal to the axis of deflection of the spring, thereby causing the assembly of tubes to exhibit multiple spring rates as they are compressed. Preferred materials for the tubes are two-part castable urethane prepared from polyether-isocyanate or polyester-isocyanate prepolymers cured with organic diamine or polyol materials.
In one embodiment of the invention described in the '916 patent, a first tube is employed that has a non-uniform wall thickness and defines a large outer diameter. A second tube is integrally molded onto the first tube and has a substantially uniform wall thickness defining a smaller outer diameter than the first tube. The first tube is positioned such that the thinnest of the non-uniform wall is adjacent to the second tube, allowing the first tube to roll over an outer peripheral surface of the second tube during compression of the spring. The above-described design provides a progressively changing spring rate whereby as the first tube collapses, a first spring rate is realized. Because of the location and configuration of the first tube, the initial spring rate is low. As the second tube is engaged and collapses, its configuration causes the spring rate to become higher and the spring stiffer. When the entire structure collapses, the spring is essentially solid and the spring rate is determined by the characteristics of elastomer from which the spring is made.
Based on the foregoing, it is the general object of the present invention to provide a spring for use in a vehicle or bicycle suspension system that overcomes the drawbacks and problems associated with known prior art suspension systems.
It is a more specific object of the present invention to provide a spring that finds utility, inter alia, in vehicle and bicycle suspension systems that exhibits a non-linear spring rate.